Reduced hippocampal volume has been consistently observed in major depressive disorder. Hippocampal volume loss is particularly evident in patients with recurrent and chronic depression. However, the reports in first episode depression have been mixed.Methods

We performed a random effects meta-analysis to establish whether hippocampal atrophy exists from disease onset. We included magnetic resonance imaging studies of hippocampal volume in patients with first episode major depressive disorder and matched healthy controls.Results

A total of 7 studies met our inclusion and exclusion criteria, representing independent observations in a total sample of 191 patients and 282 healthy controls. The cumulative analysis revealed hippocampal volume loss in patients with first episode depression relative to controls in both the left (standardised mean difference, SMD = − 0.41, 95% Confidence Interval: [− 0.78;−0.03], z = − 2.14, p = 0.0321) and right (SMD = − 0.53[− 0.98;−0.09], z = − 2.38, p = 0.0173) hippocampi. The average volume reduction was − 4.0% in the left and − 4.5% in the right hippocampus.Conclusions

Hippocampal volume loss in first episode depression is consistent with a neurodevelopmental model of depression, advocating hippocampal structure as a potential diagnostic neurobiomarker for depression.